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Old 27-06-2011, 12:26   #1
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Remedy For Seawater Getting Into Engine?

The issue of seawater back-siphoning into the engine doesn't seem to get talked about a lot, but I've read accounts from some long-distance cruisers that this can be an issue when under sail in rough seas. Although it's likely a pretty rare occurrence, esp. assuming proper siphon loops are in place in both the engine compartment and at the transom, seawater that is already in the line and/or in the muffler can apparently make its way back into the engine. Then there's the possibility, of course, of seawater back-siphoning its way in through the transom under following seas. Seems to be more unlikely on the intake side, however, assuming the seacock is closed.

While I've read of various ways to deal with it, one account suggests simply mounting shut-off valves on the discharge side of the mixing elbow. It would be more accessible (and therefore less likely forgotten) inside the engine compartment (vs. at the transom), and would eliminate the possibility of any water infiltration that remains in the line and muffler. The only downside I've uncovered is the prospect of forgetting to open before starting the engine. Even then, however, the engine will apparently just quit, assuming, of course, that you've remembered to open the intake seacock and have therefore avoided impeller damage!

It sounds like a simple solution. I MUST, therefore, be missing something. Any thoughts?
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Old 27-06-2011, 12:51   #2
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Re: Remedy For Seawater Getting Into Engine?

I would think that just downstream of the mixing elbow it would still be relatively hot and corrosive to be placing something with moving parts.

A lot of older boats have a seacock at the transom on the exhaust line. Having that and making the drain plug on the muffler accessible should take care of it.

Of course modern thinking is we're too stupid to have a valve on the exhaust line so we shouldn't do that.

John
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Old 27-06-2011, 13:20   #3
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Re: Remedy For Seawater Getting Into Engine?

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Originally Posted by cal40john View Post
I would think that just downstream of the mixing elbow it would still be relatively hot and corrosive to be placing something with moving parts.

A lot of older boats have a seacock at the transom on the exhaust line. Having that and making the drain plug on the muffler accessible should take care of it.

Of course modern thinking is we're too stupid to have a valve on the exhaust line so we shouldn't do that.

John
Yup, the assumption that we're too stupid, along with the reality that most boats rarely leave the dock, let alone encounter rough seas.

Do you think an in-line ball valve at the end of the exhaust line (nr. the transom) would work OK? Seems like installing a seacock may be a lot of work, given the application.
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Old 27-06-2011, 14:51   #4
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Re: Remedy For Seawater Getting Into Engine?

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Yup, the assumption that we're too stupid, along with the reality that most boats rarely leave the dock, let alone encounter rough seas.

Do you think an in-line ball valve at the end of the exhaust line (nr. the transom) would work OK? Seems like installing a seacock may be a lot of work, given the application.
In the 20+ years I sailed my friend's Cal 34 I only closed the seacock twice, Straits of Georgia and ocean, but except for a trip to Hawaii the boat was used in the Pacific Northwest.

I have never used the seacock on my Cal 40 (except to exercise it), but I haven't gotten outside of the PNW with my own boat yet.



Both these are inline on the hose. I never installed one, they're on boats I sail. I guess that says something about me.

John
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Old 27-06-2011, 15:54   #5
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Re: Remedy For Seawater Getting Into Engine?

The in / out lines should never be closed when the boat is under way. You may be forced to start the engine at a moment's notice one day and I would not waste that moment for opening the cocks.

I found the siphon device on the intake side and a properly looped exhaust sufficient in all and any conditions. And my boat´s freeboard is perhaps as low as it gets.

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Old 27-06-2011, 16:19   #6
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Re: Remedy For Seawater Getting Into Engine?

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The in / out lines should never be closed when the boat is under way. You may be forced to start the engine at a moment's notice one day and I would not waste that moment for opening the cocks.

I found the siphon device on the intake side and a properly looped exhaust sufficient in all and any conditions. And my boat´s freeboard is perhaps as low as it gets.

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Old 27-06-2011, 16:29   #7
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Run the engine?

In my very limited experience running the engine could be the one way to keep everything right and proper.

It'll keep everything inside nice and warm and give a little extra control over the boat as well.

Should only use a few litres an hour, maybe 150 tops in a three day storm.

Well, that and a drogue is my plan and (so far) I'm sticking to it.
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